Integrated circuits (ICs) that cannot be adequately cooled by simple exposure of the package to ambient air inside the system may employ a mechanism to remove additional heat in order to operate properly and meet reliability lifetime requirements. One mechanism is to place a metal heat sink with large surface area onto the IC. This increases the surface area exposed to air and increases the amount of heat transferred from the IC, thereby keeping its temperature below the maximum allowable. In order to efficiently remove heat, the heat sink is held in firm contact with the IC, or in firm contact with a thermal interface material (such as tape or grease) that is in contact with the IC.
Various mechanisms for securing heat sinks include using thermally conductive adhesive tape, and applying an external force to clamp together the IC and the heat sink. The external force mechanisms press down on the heat sink. An opposing upward force can be applied in various ways, including pulling up (1) under the bottom of the IC itself, (2) under the IC's socket (if one is used), and (3) under the circuit board to which the IC is mounted (regardless of whether or not a socket is used).
Heat sink mass is a factor in determining which pull-up mechanism is used. Less massive heat sinks can be secured with tape or clamping mechanisms that pull up on the IC or its socket (if used). However, larger heat sinks may require much more clamping force than these mechanisms can provide. This is because more massive parts generate greater separation forces during vibration. Larger heat sinks required for higher power devices (such as high speed processors and chipset components) may use a mechanism that pulls up on the circuit board.
One mechanism of pulling up on the circuit board is to manually insert a through hole mount (THM) anchor into plated through holes (PTHs) in the circuit board, and allow its leads (or legs) to be wave soldered when the bottom of the board is passed over a solder wave to mechanically and electrically connect all the other THM components to the board. An example of a THM anchor design is a heavy wire design in an inverted horseshoe shape, with the wire leads (or tips) inserted into PTHs in the board. The curved part of the horseshoe serves as the anchor point to which the heat sink clamping apparatus can be connected or secured. The clamping apparatus applies force in order to keep the heat sink in firm contact with the IC under static conditions and under the greater-force dynamic conditions of vibration.
Unfortunately, the static and dynamic vibration-generated forces may cause the solder joint to creep, resulting in solder cracks and eventually the failure of the anchor, which causes failure of the clamping mechanism, loss of contact between the heat sink and the IC, and ultimately the failure of the IC, the board and the system.